Re: Improving GDB startup time with large programs

[mec dot gnu at mindspring dot com (Michael Elizabeth Chastain)]

Hi Nick,

> I'm currently using 6.1 to which I have just upgraded. However, it seems
> about 15% slower at startup than 6.0 despite my expectations that it
> would be faster.

That's a bummer.  I have one large C++ program, the 'monotone'
executable, that got a lot faster (native i686-pc-linux-gnu,
red hat 8.0, gcc 3.3.something).

> I'm using g++ 3.2 with '-Wall -Wno-unused -g'

You could try upgrading to g++ 3.3.3 or g++ 3.4.0.
Basically, if you have a lot of disk space, and you configure
the compiler with '--prefix=...', you can play with different
compilers.

I have no reason to think that will actually help any, though.

> How do I profile gdb?

When you build gdb, configure as normal.
Then use this command to build:

  make CFLAGS='-pg'

Then install as normal.

(As you might already know, experimenting with different versions of gdb
is a lot easier and safer if you use --prefix=... when configuring it.
I have dozens of gcc's and several gdb's on my system at any time).

Then run the new gdb as you normally would on your test program.
Make sure to quit gdb cleanly at the end.

Look for a file named 'gmon.out'.  This is the data file from the
profiler.  Then run 'gprof /path/to/installed/bin/gdb' to see the
output.  It will have this kind of format:

  Flat profile:

  Each sample counts as 0.01 seconds.
    %   cumulative   self              self     total
   time   seconds   seconds    calls  ms/call  ms/call  name
   16.67      0.01     0.01   175396     0.00     0.00  symbol_natural_name
   16.67      0.02     0.01    27446     0.00     0.00  htab_find_slot_with_hash
   16.67      0.03     0.01    15575     0.00     0.00  read_partial_die
   16.67      0.04     0.01      146     0.07     0.10  dwarf2_read_abbrevs
   16.67      0.05     0.01        7     1.43     1.98  find_methods
    8.33      0.06     0.01     6466     0.00     0.00  xrealloc
    8.33      0.06     0.01       31     0.16     0.16  xcalloc

  ...

Now, if you can do this for gdb 6.0 versus gdb 6.1, and report the
top 15-20 lines of the profile output, that would be interesting data.
And then there's the CVS version of gdb.

Michael C